Equation of Cardioid
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Theorem
Polar Equation
Let $C$ be a cardioid embedded in a polar coordinate plane such that:
- its deferent of radius $a$ is positioned with its center at $\polar {a, 0}$
- there is a cusp at the origin.
The polar equation of $C$ is:
- $r = 2 a \paren {1 + \cos \theta}$
Parametric Equation
Let $C$ be a cardioid embedded in a Cartesian coordinate plane such that:
- its deferent of radius $a$ is positioned with its center at $\tuple {a, 0}$
- there is a cusp at the origin.
Then $C$ can be expressed by the parametric equation:
- $\begin {cases} x = 2 a \cos t \paren {1 + \cos t} \\ y = 2 a \sin t \paren {1 + \cos t} \end {cases}$